Deadlock

For example, consider two transactions T1 and T2:

• Transaction T1 holds a lock on resource A and needs a lock on resource B to proceed.

• Transaction T2 holds a lock on resource B and needs a lock on resource A to proceed.

In this scenario, neither transaction can continue because each is waiting for the other to release the lock it needs. This is a deadlock.

Deadlocks are problematic because they can lead to system inefficiencies and delays. If not handled, they can leave transactions in a state of perpetual waiting, consuming system resources and possibly causing the system to become unresponsive.

Deadlock management in a database system is generally carried out in one of the following ways:

1. Deadlock Prevention: This strategy involves designing the system in a way that makes it impossible for deadlocks to occur in the first place. This typically involves enforcing rules about the order in which locks can be obtained. For example, a system might require that all locks be obtained at once at the beginning of a transaction.

2. Deadlock Avoidance: This strategy involves the system making a check before granting a resource request to see if granting the request could potentially lead to a deadlock situation.

3. Deadlock Detection and Recovery: In this approach, the system allows deadlocks to occur, but it also has a way of detecting them when they do. Once a deadlock is detected, the system can take steps to recover from the deadlock, such as by aborting one or more of the transactions involved in the deadlock and releasing their resources.

Deadlock management is a complex aspect of database system design, and the best approach may depend on various factors, including the specific workload and performance requirements of the system.